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Author Topic: Atrium smoke extract  (Read 2171 times)

ahmedshawky31297

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Atrium smoke extract
« on: March 24, 2015, 06:33:24 am »

Hi guys,
I wonder if someone can help me with my simulation on smoke extract from an atrium having an area of 400 m², a height of 8 meters and having a HRR fire of 2000 KW.
The smoke is extracted from the top level at a rate of 13.2 M³/S as per NFPA 92B calculations to form a clear smoke height of 4 M and air inlets are at a level lower than the 4 meters by 2 meters at least and at a velocity of 1 m/s.
Yet the smoke level is always descending till smoke fills the space.
On increasing the extract rate to up to double the above mentioned quantity, i.e. 28.3 M³/S, the smoke layer was preserved at 4 meters height.
am I doing something wrong, as I can not tolerate the idea that the NFPA might not be correct.
I am using the mesh as my building boundary for simplicity and the air inlets are open vents in the mesh.

Please advise.
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Dave McGill

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Re: Atrium smoke extract
« Reply #1 on: March 24, 2015, 11:10:56 am »

Hi,

It's hard to diagnose without having your .psm file.

I suggest you add air volume measuring devices to ensure that the volume being extracted is what you think it is.

Having the air inlets for the building on the boundary is not a good idea. There will be a much more realistic air flow in you include the building walls with openings, and at least 1-2 m space between the openings and the domain boundary.

Dave
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Dave McGill
firemodel.ca

rahuljindal.66

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Re: Atrium smoke extract
« Reply #2 on: April 07, 2015, 02:50:14 am »

HI Ahemed,

As per my experience you are not doing anything wrong, because I faced the same issue and after discussing some senior technical persons I came to know that the calculation according the code does not consider your actually geometry, these calculations are for simple geometry which is never in the real case. So these calculations can be taken as your reference but actual flow rate can be given by CFD analysis only. That is why CFD analysis is carried out. but as Dave suggested , confirm that the flow is passing through the exhaust as you specified.
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